In the case of such a structure that a body of a fuel injection valve is inserted and attached into an attachment hole formed at a predetermined position of an internal combustion engine, there is required a prevention of a leakage of gas in a fuel injection space (e.g., inside a combustion chamber or an intake pipe) through a clearance between an inner peripheral surface of the attachment hole and an outer peripheral surface of the body.
Accordingly, an annular seal material is conventionally disposed in this clearance. Specifically, a radially-recessed reduced diameter part is formed on the outer peripheral surface of the body, and the body is inserted into the attachment hole with the seal material attached to this reduced diameter part (see JP-A-2005-155394).
The inventors have considered forming a tapered part on a part of the outer peripheral surface of the body on an opposite side of the reduced diameter part from a nozzle hole. This tapered part has such a shape that a diameter size of the body increases gradually in a direction further on the opposite side from the nozzle hole. Accordingly, in a use state where gas pressure is applied from the nozzle-hole side of the seal material, when the seal material is pushed up toward the opposite side from the nozzle hole by this gas pressure, the seal material is clamped between the inner peripheral surface of the attachment hole and the tapered part. As a result, a compressive deformation of the seal material in its radial direction is promoted, so that the surface pressure of the seal material increases (this phenomenon is hereinafter referred to as a wedge effect). For this reason, sealing properties by the seal material improve.
As a taper angle of the tapered part becomes smaller, the seal material has a greater wedge effect to increase the effect of the improvement in sealing properties. However, if the taper angle is made excessively small, there is a concern about damage to the seal material as described below.
Specifically, when the fuel injection valve is attached at the predetermined position of the engine by inserting its body into the attachment hole of the engine, the seal material is scraped against the inner peripheral surface of the attachment hole and receives frictional force, so that the seal material may be rubbed up and displaced to the opposite side from the nozzle hole. Although the tapered part operates to limit the displacement of the seal material, the tapered part has less effect of limiting the displacement as the taper angle is made smaller. When the displacement of the seal material becomes excessively large, the above-described surface pressure by the wedge effect unduly rises. If the body further continues to be inserted into the attachment hole in this state, the seal material is torn up and damaged.
In short, there is a trade-off relationship between the improvement of sealing properties by the wedge effect by decreasing the taper angle, and the limitation of the displacement of the seal material by increasing the taper angle.